Installing and uninstalling wordpress themes for better user experience is a common characteristics on wordpress enable blogs.

It is learnt that whenever we install a new theme the thumbnail size supported by the new theme does not properly match the exact dimension of your new image size. Hence wordpress automatically adjust the image size.

So where is the problem you can say? The problem is, if you have selected a different thumbnail size i,e 150x150px in general setting, all your uploaded image will be resized by the default wordpress engine into 150x150px and this thumbnail size will be used by the featured image box. if your theme display 100x100px as a featured image then your theme will resize all your images from 150x150px into 100x100px. thus increase the loading size.

Another issue, Suppose your theme support 100x100px size featured image , so you adjust general setting to match your theme, but what about the previously generated thumbnails. These previously resized thumbnail remains in the same size.

To overcome these this simple problem, there is two solution –

First Solution – How to Regenerate Post Thumbnails

Download all previously Generated Thumbnail using some FTP software from image folder.

Resize them into your new size using any photo editing tool like Photoshop. Youtube has a lots of quality tutorial on photo resizing.

Upload all these newly resized photo into their respective folder/folders.

How to use Regenerate Plugin

Install the plugin. : You can install the same plugin using any of the method listed in the installation section i,e either upload the unzipped file in the /wp-content/plugin folder or use add new plugin option from Admin Panel. I think you do not need to know how to install plugin. Though its detailed information is already given on its download page

Now this plugin will try to regenerate all your previously generated thumbnail. It may take from few minutes to few hours depends on your image count.

Screenshot are here showing it’s feature

Advantage of Regenerated Thumbnails

The main advantage of these newly regenerated thumbnails are they are according to your new themes settings thus there is no need to resize your image, Hence your theme is now ready to render your website more speedy.

major Disadvantage of Regenerated Thumbnails

The main and major disadvantage of this plugins – it does not regenerate any old image instead of that it recreate a new image from your original image and store in the same image folder with your new image settings.

Another major disadvantage of this plugin – if you have restart the regenerator any how two times. it will create two new files with the same dimension.

To sum up its disadvantage you are now having multiple copies of the same old files. So to save some micro seconds, you added some hundred MB in your account extra.

Conclusion

Overall a great plugin to regenerate old generated thumbnails and medium size images from your original image.

It is always advised to seek professional bloggers advise before you choose your theme or going to start installing wordpress for your blog.

If you missed both of them and very conscious about the loading time of your blog and do not know how to resize your images using photo-shop, then definitely go for this image resize plugin.

But every time you upload an image wordpress generate multiple copies of the same image according to the setting and theme functionality. So my advice is always take help of a pro before choosing a theme or setting your wordpress. Thanks for posting your concern vivek.